3. Observe: Place the next two tRNA molecules on the mRNA strand. What happens?

As each tRNA molecule binds to the mRNA, the ribosome joins the amino acid carried by the tRNA to the growing amino acid chain.

4. Describe: UAG (as well as UAA and UGA) is an example of a stop codon. Molecules called release factors bind to stop codons. Place the release factor on the mRNA molecule.

What happens?

Gene expression is a multi-step process. Place these events in the correct order.

Question 13 options:

charged tRNA molecules read the next codon, entering the A site of the ribosome.

Translocation of the mRNA to the cytoplasm.

Recruitment of RNA polymerase.

tRNA(Met) binds to the start codon AUG in the P site of the ribosome.

Assembly of small and large ribosome subunits on the mRNA.

Processing of the primary RNA molecule.

Release factors recognize the stop codon, signaling the release of the protein, mRNA and ribosome subunits.

Synthesis of primary RNA molecule, a direct copy of the DNA template.

Recognition of the mRNA by the small ribosome subunit .

Peptidyl transferase, transfers the amino acid of the incoming tRNA to the growing peptide chain.

Binding of transcription factors to the promoter.

What happens when a stop codon is reached by a ribosome?

A termination tRNA^ter binds to the codon and the growing peptide is transferred to it. When the peptidyl-tRNA^terreaches the P site, the ribosome is signaled to release the protein. The ribosome then is likely to dissociate.

A release factor binds to the codon and is used to release the growing peptide from the P site tRNA.

A termination tRNA^ter binds to the codon and the growing peptide is transferred to it. When the peptidyl-tRNA^terreaches the P site, the ribosome dissociates. A separate peptidyl transferase then releases the protein from tRNA^ter.

A release factor binds to the codon and the ribosome dissociates. A separate peptidyl transferase then releases the protein from the last tRNA to which was attached.

A termination tRNA^ter binds to the codon and is used to release the growing peptide from the P site tRNA. The ribosome then is likely to dissociate.

Facts about ribosomes

Indicate whether each of the following statements aboutribosomes is true or false.

1. Ribosomes are composed of tRNA and protein. TrueFalse
2. During translation in eukaryotes, some ribosomes remain free inthe cytoplasm while others attach to protein channels embedded inthe RER. TrueFalse
3. During initiation of translation, the small ribosomal subunitjoins to the mRNA and initiator rRNA, followed by the largeribosomal subunit. TrueFalse
4. When a ribosome first assembles on the mRNA, the initiator tRNAoccupies the A site while the P and E sites are empty.TrueFalse
5. During translation, a charged tRNA first binds to the ribosomeif its anticodon matches the codon in the E site. TrueFalse
6. A peptide bond forms between the amino acid attached to a tRNAin the A site and the growing polypeptide attached to a tRNA in theP site. TrueFalse
7. Uncharged tRNA molecules in the E site are ejected from theribosome. TrueFalse
8. No more than 2 tRNA molecules are bound to a ribosome at anygiven time. TrueFalse
9. During translocation of the ribosome, tRNA molecules move fromthe P site, to the A site, to the E site, and are then ejected fromthe ribosome. TrueFalse
10. During translation, an amino acid attached to a tRNA in the Asite is transferred to a growing polypeptide attached to a tRNA inthe P site. TrueFalse